This ResourceHandler implementation will remove all separate script and stylesheet resources which have the
target attribute set to "head" from the UIViewRoot and create a combined one
for all scripts and another combined one for all stylesheets.

This ResourceHandler implementation allows the developer to map JSF resources on an URL pattern of
/javax.faces.resource/* (basically, the value of ResourceHandler.RESOURCE_IDENTIFIER) without
the need for an additional FacesServlet prefix or suffix URL pattern in the default produced resource URLs,
such as /javax.faces.resource/faces/css/style.css or
/javax.faces.resource/css/style.css.xhtml.